I am facing a memory conflict I think.

Well I have a Celeron 1,8 GHz with 3 slots.\

I used to have a DDR 256Mb - 266MHz
and a DDR 256Mb -333MHz memory.

I bought one more 512Mb - 400MHz.

My first 2 chips worked at 266MHz of course.

Well when I put the new one my computer crashed. It didn't worked even with the only the new one.

I read the m/b manual and it can take upto 3 chips upto 266MHz or 2 upto 333MHz.

I configured from BIOS to function at 300MHz with 2 chips (the 333 and 400MHz) since at 333MHz I noticed some strange bahaviour.

This worked for some days but yesterday it stopped function. My father was at winXP and I figured it's a win problem but when I switched to Fedora it worked badly and then it stopped completely.

My question is why it doen't function with these settings. I mean it's supported by the motherboard. Are there many technologies in memory chips.

Sounds more like your newer chip is fried.

Download knoppix, put the ram in your computer such that the slowest chip is in the slot closest to the processor. Put in all your ram, so the fastest is further away (this is because the chip closest is often considered primary and the bios will pay particular attention to that).

Once you have all the ram in then fire up knoppix and run memtest.

Ive never had a problem with speed mismatches. So it sounds like bad ram to me.

Regards
-Rob